To understand the bicycle controversy in San Francisco, consider the concept of bike sharing.

In theory it is a lovely idea - utopian, trendy and green. With a swipe of a card, commuters could rent a bike and ride to the office, a restaurant or the store. Once there, they'd dock the bike and stroll away, leaving it for the next bike sharer. In Paris, supporters say, it works like a dream.

In reality, there are some kinks. After a year, Washington's SmartBike program found that more than 60 percent of renters used a bike less than once a week. Montreal's bike program cost $23 million to research and launch, and the 5,000-bike fleet has experienced plenty of problems with vandalism and theft.

San Francisco's pilot program, a mere 50 bikes at a cost of $500,000, is being mocked for being too timid and small. Paris has 20,000 bikes (although reports indicate that as many as 7,800 have been stolen).

The bike-friendly city debate has fractured into lawsuits, name-calling and the inevitable rowdy meetings at City Hall - essentially losing sight of the middle ground that could lead to more reasonable and realistic bike policies.

How did it get to this point? The same way as always: opposing groups of people who are absolutely, positively convinced they are right.

Andy Thornley, the eminently reasonable San Francisco Bicycle Coalition program director, says the city has spent years making itself car friendly, and "now we should shape the city back to make it more convenient to walk or ride a bike."

Not a bad idea. New bike lanes, safe routes and more places to lock up a bike would all be welcome improvements.

Unfortunately, the true believers have gone at it in such a ham-fisted way that it has cost them supporters. Katy Liddell, a bicyclist in her 60s who is a proud member of the Bicycle Coalition, has filed an appeal to the bicycle plan's environmental impact report.

Liddell says eliminating left turns on Second Street would create more traffic, backups and pollution.

"They never came to ask for input until the last minute," she said, "and then they did not like what we had to say."

Meanwhile, curmudgeonly local resident and blogger Rob Anderson has been vilified in bike chat groups - and written up in the Wall Street Journal - for his opposition to what he likes to call "the bicycle fantasy." Anderson's lawsuit, demanding the environmental review for the bicycle plan, put everything on hold for three years.

The report was upheld Tuesday at the Board of Supervisors meeting, which means there will be fewer parking places and lanes for cars, and public transportation will probably be slowed. (There was an acknowledgement that the Second Street plan needs further study, given the neighborhood opposition.)

At the core of this is a simple proposition: the wishes of the few versus the needs of the many. There are a lot of bicyclists in San Francisco. But there are far more drivers and public transit commuters.

Want a cheap, easy way to get to the office? We have one. It is called a bus. The Municipal Transportation Authority says some 700,000 trips are taken on public transit in the city every work day.

Thornley likes to envision the day when bike travel in the city is not just "for young, athletic, thrill-seeking me." He insists he's seeing more moms in dresses and businessmen in suits pedaling to work. So far I've missed them.

What I do see are a lot of bicyclists riding to work in the mornings, even on the demolition derby run that is Market Street. Great, and I'd definitely support more places to lock up their bikes. But the idea of significantly reconfiguring the city isn't realistic.

There's a way to make this work, but it isn't to block an intersection with bikes while chanting, "Whose street? Our street!"

Liddell says she's sure it can be settled without all the conflict.

"We just need a little more time," she said. "Just a little give and take on both sides."

Unfortunately, giving a little is not something that happens often here. Not when people are absolutely, positively convinced they are right.